The more common internal vaporization engines, for example, steam engines, utilize water which requires relatively high temperatures to be changed from the liquid to the vapor state and provide the motive force to the engine. Other engines have been developed which utilize much lower boiling point liquids such as dichlorodiflouromethane (CCL.sub.2 F.sub.2) also known as Freon 12 and commercially obtainable from the Dupont Company. An example of an engine of this general type is shown and described in U.S. Pat. No. 2,513,692 issued on July 4, 1950 to C. L. Tubbs for "Vapor Engine Driven by Expansion and Contraction of Vapor". Other engines have been developed which take advantage of the availability of solar heat to be used in conjunction with a working fluid circuit. An example of this type of engine and control system is shown and described in U.S. Pat. No. 3,916,626 issued to G. O. Schur on Nov. 4, 1975, for "Thermally Powered Generating System Employing a Heat Vapor Bubble Engine". Still other power generating systems and engines have been developed which utilize the temperature differential between the surface region and lower regions of the earth or as otherwise stated utilize naturally occurring geothermal temperature differences in their operating systems.